Magnet system for travelling wave tubes



06L 1960 c. T. DE WIT ,956,193

MAGNET SYSTEM FOR TRAVELLING WAVE TUBES \L\\"\\\\\ \\\\\\\\i\ W A 2 QQ B A? a? 1- z H61 4 NNNNNN o R 1 2CORNELIS TEUNIS DE wrr Oct. 11, 1960 c. T. DE wn' MAGNET sysmx FOR TRAVELLING WAVE TUBES 3 Sheets-Sheet 2 Filed June 13, 1958 INVENTOR CORNELIS TEUNIS DE WIT AGE C. T. DE WIT MAGNET SYSTEM FOR TRAVELLING WAVE Oct. 11, 1960 3 Sheets-Sheet 3 Filed June 13. 1958 fi w N m unnnz w m x FIG.5

mvzm-on CORNELIS TEUNIS DE WIT GEN United States Patent MAGNET SYSTEM FOR TRAVELLING WAVE TUBES Cornelis Tennis de Wit, Eindhoven, Netherlands, as-

signor to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed June 13, 1958, Ser. No. 741,871

Claims priority, application Netherlands July 11, 1957 i '3 Claims. c1. 313-s4 This invention relates to a magnet system for a travelling-wave tube comprising two sets of radially arranged rods which are permanently magnetized in opposite radial directions, these radial sets or stars being arranged coaxially with one another at a slight distance from one another while their outer ends are connected by axial soft iron closing parts, pole pieces being provided at the inner ends.

In the known magnet systems of the above-described construction, in order to ensure a sufficient uniformity of the axial field it is required to connect the two pole pieces by means of a soft iron housing for the travelling wave tube. Due to the presence of the tubular soft iron housing 'a considerable part of the magnetic induction does not contribute to the concentration of the electron beam in the tube while furthermore the field remains far from uniform in the direction of length.

It is an object of the present invention to provide a construction which offers advantages over the known constructions.

According to the invention, in a magnet system for a travelling-wave tube comprising two sets of radially arranged rods which are permanently magnetized in opposite radial directions, which sets or stars are arranged coaxially with one another at a slight distance from one another while their outer ends are connected by axial soft iron closing parts, pole pieces being provided centrally of both stars, provision is made, at a slight distance from at least one of the two permanently magnetized stars, parallel thereto and within the magnet system, of a star of permanent-magnetic material which is magnetized in the same sense and has a strength such that at this side the magnetic fields has a uniform variation in the axial direction while this star links up with the soft iron closing parts on the outside.

According to the invention, preferably provision is made, in the vicinity of the two stars of permanently magnetized material, of an additional star of magnetic material so that the magnetic field has a uniform variation in the axial direction at both ends. If a stronger field is required at the output end of the travelling-wave tube, for example in a high-powertube, at this end either the two stars can be joined or the magnetic star can be made heavier.

In order that the invention may readily be carried out, two embodiments thereof will now be described, by way of. example, with reference to the accompanying drawings, in which Figures 1 and 2 are cross-sectional views of the known magnet system and Fig. 3 shows the associated field variation in the axial direction, while 2,956,193 Patented Oct. 11, 1960 Figures 4 and 5 show magnet systems in accordance with the invention, and

Fig. 6 again shows a field variation.

In Figures 1 and 2, reference numeral 1 denotes permanently magnetized rods arranged so as to form fourpointed stars, one at each end of a magnet system the pole pieces of which are designated 2 and 3 respectively. Soft-iron closing parts are designated 4.

The arrows show the direction of magnetization. In Fig. 3, the solid curve shows the value of the magnetic field Bz in the axial direction in the axis, without the tubular soft-iron casing, as a function of the position. In Fig. 4, parts corresponding to those of Fig. 1 are designated similarly, the additional rods of magnet steel in accordance with the invention being denoted by 5. In this embodiment, the soft-iron tubular casing, which in the known arrangements is also required to reduce the radial field, is replaced by a stack of thin mu-metal rings 6 of 0.2 mm. alternating with thicker rings of hard paper 7 of thickness about 3 mms. This construction is known per se for avoiding radial fields in travelling-wave tubes. The axial field is hardly modified. Between the stack of rings 6 and 7 and the pole pieces room is left for the input and output wave guides. The associated field variation is shown by a broken line in Fig. 3. Fig. 5 shows a construction in accordance with the invention in which the field is increased at the output side of the travellingwave tube by using at this end magnet rods which are slightly longer and thicker. Fig. 6 shows the associated field variation.

What is claimed is:

1. An electron-beam concentrating magnet system for a travelling wave electron discharge tube comprising two coaxial spaced apart sets of radially positioned rods of ferromagnetic material permanently magnetized in opposite radial directions and soft ferromagnetic members connecting the outer ends of the rods, a third set of radially positioned rods of ferromagnetic material located intermediate and adjacent one of the other two sets, said third set of rods being permanently magnetized in the same radial direction as the adjoining set of rods and having a field strength at which the magnetic field strength between the first two sets has a uniform variation of field strength in the axial direction therebetween, said third set of rods being connected to said soft ferromagnetic members connecting said first two sets of rods.

2. A magnet system as claimed in claim 1 in which an additional set of rods, permanently magnetized in an opposite radial direction is located intermediate and adjacent the other of the first two sets of rods.

3. A magnet system as claimed in claim 1 in which one of said first two sets of rods is constituted of rods having thickness and length greater than that of the rods constituting the other sets, which set is located at the end of the magnet system from which the electron beam emerges.

References Cited in the file of this patent UNITED STATES PATENTS 2.825,840 Iskenderian -1 Mar. 4, 1958 2,844,750 Veith et al. July 22, 1958 2,844,754 Ciofii July 22, 1958 2,876,373 Veith et al Mar. 3, 1959 FOREIGN PATENTS 748,946 Great Britain May 16, 1956 

